The invention relates to an exhaust system of an internal combustion engine with two exhaust lines, of which each includes two catalytic converters and a valve for controlling the exhaust gas flow through the exhaust lines.
DE 197 40 702 C1 discloses an exhaust system for an internal combustion engine with two catalytic converters arranged in an exhaust duct so that they can be placed in series by a valving structure.
Furthermore, exhaust systems are known which include two separate exhaust ducts. Each exhaust duct includes two catalytic converters; one disposed closely adjacent the engine, a so-called fire wall catalytic and one disposed below the vehicle floor, a so-called underfloor catalytic converter. In order to achieve a high exhaust gas conversion rate, particularly in the two catalytic converters near the engine, it is important that the fire wall catalytic converters reach their operating temperature or, respectively, conversion temperature as rapidly as possible. During the starting phase, particularly the start-up phase of the internal combustion engine, the temperatures of the fire wall catalytic converters so far could not be increased rapidly enough so that the exhaust gases of the internal combustion engine could not be cleaned up sufficiently during the starting phase.
It is the object of the present invention to provide an exhaust system for an internal combustion engine in which the catalytic converters reach their operating temperature rapidly after start-up of the engine so that exhaust emissions during the start-up phase of the engine, particularly during a cold start, are substantially reduced.
In an exhaust system for an internal combustion engine having two groups of cylinders with a separate exhaust line for each cylinder group, each including an upstream catalytic converter and a downstream catalytic converter and a control valve, a first transverse connection extending between the exhaust lines upstream of the upstream catalytic converters and a second transverse connection extending between the exhaust lines between the upstream and downstream catalytic converters, the valves are so arranged and controlled that, during engine warm-up, the exhaust gases from both cylinder groups flow through the upstream catalytic converter of one and the downstream catalytic converter of the other exhaust line for rapid heat up of one of the catalytic converters in each of the exhaust lines.
With the arrangement according to the invention, the respective catalytic converters can be heated very rapidly so that they are rapidly activated and the engine emissions are reduced to a low level soon after engine start-up.
The invention will be described below in greater detail on the basis of the accompanying drawings.